Figure 4

Schematic structural organization of the four main categories of group I introns observed in myxomycete rDNA. (A) Self-splicing and mobile introns with homing endonuclease genes (HEGs). (B) Self-splicing all-ribozyme introns without HEG. (C) Optional host-dependent introns with structural extensions available for host factors (green), here exemplified as associated with P8. (D) Obligatory host-dependent introns with large extension either associated with host factors and/or containing direct repeats (P9) or other motifs with the potential for being regulatory RNA domains (pink). HEG: homing endonuclease gene; rDNA: ribosomal DNA.